Magnetic detection device including resistance adjusting unit

ABSTRACT

In a magnetic detection device for obtaining an output from between a variable resistance element using the magnetoresistance effect and a reference resistance element, a balance between resistance values in the device can be easily adjusted in a wide range. A voltage is applied to a resistance adjusting unit, a reference resistance element, and a variable resistance element, which are serially connected, and is also applied to another variable resistance element, another reference resistance element, and another resistance adjusting unit, which are serially connected. When subjected to a magnetic field of a predetermined size, resistance values of the variable resistance elements change, and as a result, the potentials of output terminals change. Each of the resistance adjusting units includes serially connected parallel portions each including a plurality of parallel connected resistance elements. The resistance value of the resistance adjusting unit can be changed by bringing one of the parallel connected resistance elements into a non-conduction state.

This patent document claims the benefit of Japanese Patent ApplicationNo. 2006-245420 filed on Sep. 11, 2006, which is hereby incorporated byreference.

BACKGROUND

1. Field

The present embodiments relate to a magnetic detection device fordetecting an external magnetic field by detecting a change of theresistance value of the device, and in particular, an object of thepresent invention is to provide a magnetic detection device havinghighly accurate magnetic detection by adjusting the resistance value.

2. Description of the Related Art

Usually, to detect a change of an external environment by using avariable resistance element whose resistance value is changed by theexternal environment, the variable resistance element is connected inseries to a reference resistance element whose resistance value does notchange, and the thus serially connected variable resistance element andreference resistance element are subjected to a direct current voltage.Then, a midpoint potential between the variable resistance element andthe reference resistance element is detected. Thereby, the change of theresistance value of the variable resistance element can be accuratelydetected without being affected by the environmental temperature.

In this type of magnetic detection device, it is necessary to adjust themidpoint potential between the variable resistance element and thereference resistance element by adjusting the resistance value of thereference resistance element. The midpoint potential is preferably setto be one half the value of a power supply voltage.

As described in Japanese Unexamined Patent Application Publication Nos.2001-35702 and 2001-44001, a conventional method of adjusting theresistance value is performed by forming a resistance element on asubstrate and thereafter removing a part of the resistance elementthrough trimming.

In the resistance value adjusting method described in the abovepublications, resistive films formed into square frames are partiallyremoved. However, the resistive films positioned on the respective sidesof each of the squares all have the same resistance value. Thus, whenany one of the resistive films is trimmed, the amount of change of theoverall resistance value is small. It is therefore difficult to obtain awide adjustment range of the resistance value.

Further, to obtain the wide adjustment range of the resistance value, itis necessary to provide a large number of the square frames formed bythe resistive films, as described in Japanese Unexamined PatentApplication Publication No. 2001-44001. Furthermore, to trim theresistive films, it is necessary to calculate the positions of theresistive films to be removed by using a complicated formula. As aresult, the structure of the resistive films for adjusting theresistance value becomes complicated, and the adjustment operation ofthe resistance value also becomes complicated.

SUMMARY

In light of the above-described problems associated with conventionaltechniques, it is an object of the present invention to provide amagnetic detection device capable of obtaining a wide adjustment rangeof the resistance value and permitting easy adjustment of the resistancevalue.

The present invention provides a magnetic detection device in which avariable resistance element having an electrical resistance changed byan external magnetic field and a reference resistance element having anelectrical resistance not changed by the external magnetic field, areserially connected to each other and applied with a direct currentvoltage to detect a midpoint potential between the variable resistanceelement and the reference resistance element. In the magnetic detectiondevice, at least one of the variable resistance element and thereference resistance element are serially connected to a resistanceadjusting unit including a plurality of serially connected parallelportions, each of which includes a plurality of parallel connectedresistance elements, and which are different from one another incombined resistance value. The sum of the combined resistance values ofthe resistance adjusting unit is adjusted by bringing any one of theresistance elements into a non-conduction state.

In the magnetic detection device according to the present invention, theplurality of the parallel portions are connected in series and aredifferent from one another in combined resistance value. Therefore, thesum of the combined resistance values of the resistance adjusting unitcan be changed in a wide adjustment range by selecting a resistanceelement of any one of the parallel portions and bringing the resistanceelement into a non-conduction state.

In a later-described embodiment of the present invention, two resistanceelements are connected in parallel in each of the parallel portions.Alternatively, three or more resistance elements may be connected inparallel in each of the parallel portions. In this case, it is possibleto perform such an adjustment that the resistance elements included inone parallel portion excluding one of the resistance elements are allbrought into the non-conduction state.

In the present invention, it is preferable, for example, that theresistance adjusting unit includes a plurality of resistive layersextending parallel to one another and connected to one another byconductive layers at a plurality of positions, and that parts of theresistive layers sandwiched by an adjacent pair of the conductive layersform the resistance elements forming one of the parallel portions. It ispreferable that the parallel portions are made different from oneanother in combined resistance value by differently setting intervalsbetween the conductive layers, and that the sum of the combinedresistance values of the resistance adjusting unit is adjusted bydisconnecting the resistance element at a position between the adjacentpair of the conductive layers.

In the above-described configuration, the resistance adjusting unit canbe easily formed by forming the resistive layers extending parallel toone another and by establishing conduction between the resistive layersat the plurality of positions by using the plurality of the conductivelayers. Further, the combined resistance values of the respectiveparallel portions can be individually set by varying the intervalsbetween the conductive layers.

In the present invention, it is preferable, for example, that thevariable resistance element is a magnetoresistance effect element, andthat each of the resistive layers forming the resistance adjusting unitis formed by the same film materials as film materials forming themagnetoresistance effect element, and is determined in lamination orderof the film materials to prevent the resistance value thereof from beingchanged by the external magnetic field.

If the resistance adjusting unit is formed by the same materials as thematerials forming the variable resistance element, it is possible toequalize a characteristic change caused by a temperature change betweenthe resistance elements of the resistance adjusting unit and thevariable resistance element.

In the present invention, it is preferable, for example, that each ofthe parallel portions is configured such that the plurality of theresistance elements included therein are the same in resistance value,and that the combined resistance value thereof is increased in a phasedmanner in the serial direction of the resistance adjusting unit. Thusconfigured, the degree of adjustment can be accurately recognized in theadjustment of the resistance value of the resistance adjusting unit.

In the above case, it is preferable in the present invention that thecombined resistance value of one of a pair of the parallel portionsadjacent to each other in the serial direction is twice as great as thecombined resistance value of the other one of the pair.

With the combined resistance value thus set to be doubled from one ofthe adjacent pair of the parallel portions to the other one of the pair,the adjustment range of the resistance value adjusted by the resistanceadjusting unit can be increased by bringing any one of the resistanceelements into the non-conduction state. Further, the resistance valuechanged by the adjustment can be accurately recognized.

According to the present invention, the resistance value can be easilyadjusted, and a wide adjustment range of the resistance value can beobtained. Accordingly, a good balance can be set between the resistancevalue of the variable resistance element and the resistance value of thereference resistance element connected in series to the variableresistance element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a magnetic detection device accordingto an embodiment of the present invention;

FIG. 2A is a cross-sectional view of a variable resistance element;

FIG. 2B is a cross-sectional view of a reference resistance element;

FIG. 3 is a circuit diagram of the magnetic detection device;

FIG. 4 is a circuit diagram illustrating a resistance adjusting unit;and

FIG. 5 is an explanatory diagram illustrating adjustment phases andadjustment ranges of the resistance adjusting unit.

DETAILED DESCRIPTION

FIG. 1 is a plan view of a magnetic detection device according to anembodiment of the present invention. FIG. 2A is a cross-sectional viewof a variable resistance element, and FIG. 2B is a cross-sectional viewof a reference resistance element. FIG. 3 is a circuit diagram of themagnetic detection device shown in FIG. 1. FIG. 4 is a circuit diagramillustrating details of a resistance adjusting unit.

A magnetic detection device 1 is formed on a surface of a substrate 2 bya thin film process. As illustrated in the circuit diagram of FIG. 3,the magnetic detection device 1 includes a first resistance adjustingunit 3, a first reference resistance element 4, a first variableresistance element 5, a second variable resistance element 6, a secondreference resistance element 7, and a second resistance adjusting unit8.

As illustrated in FIG. 1, the surface of the substrate 2 is providedwith a power supply terminal 11. The power supply terminal 11 isconnected to one end of the first resistance adjusting unit 3 via a leadlayer 12 a and to one end of the second variable resistance element 6via a lead layer 12 b.

The first resistance adjusting unit 3, the first reference resistanceelement 4, and the first variable resistance element 5 are connected inseries, and the other end of the first variable resistance element 5 isconnected to an earth terminal 13. Meanwhile, the second variableresistance element 6, the second reference resistance element 7, and thesecond resistance adjusting unit 8 are connected in series, and theother end of the second resistance adjusting unit 8 is connected to theearth terminal 13. Further, a connection midpoint between the firstreference resistance element 4 and the first variable resistance element7 is connected to a first output terminal 14. Meanwhile, a connectionmidpoint between the second variable resistance element 6 and the secondreference resistance element 7 is connected to a second output terminal15.

FIG. 2A is the cross-sectional view illustrating the first variableresistance element 5 and the second variable resistance element 6 cutalong a plane extending in the directions of X1 and X2. The firstvariable resistance element 5 and the second variable resistance element6 are the same in lamination structure.

Each of the first variable resistance element 5 and the second variableresistance element 6 is a magnetoresistance effect element using thegiant magnetoresistance effect. The magnetoresistance effect element isformed into a film, with an antiferromagnetic layer 21, a fixed magneticlayer 22, a nonmagnetic conductive layer 23, and a free magnetic layer24 laminated on the substrate 2, in this order. A surface of the freemagnetic layer 24 is covered by a protective layer 25.

The antiferromagnetic layer 21 is formed of an antiferromagneticmaterial such as an Ir—Mn alloy (an iridium-manganese alloy). The fixedmagnetic layer 22 is formed of a soft magnetic material such as a Co—Fealloy (a cobalt-iron alloy). The nonmagnetic conductive layer 23 isformed of Cu (copper), for example. The free magnetic layer 24 is formedof a soft magnetic material such as a Ni—Fe alloy (a nickel-iron alloy).The protective layer 25 is a layer formed of Ta (tantalum).

In each of the first variable resistance element 5 and the secondvariable resistance element 6, the magnetization direction of the fixedmagnetic layer 22 is fixed due to the antiferromagnetic coupling betweenthe antiferromagnetic layer 21 and the fixed magnetic layer 22. In thepresent embodiment, the magnetization direction of the fixed magneticlayer 22 is directed and fixed in the direction of X2. Further, thefixed magnetic layer 22 and the free magnetic layer 24 are magneticallycoupled to each other with the interposition of the nonmagneticconductive layer 23. Thus, when there is no action by an externalmagnetic field, the magnetization direction of the free magnetic layer24 is directed and stabilized in the direction of X2.

As illustrated in FIG. 1, each of the first variable resistance element5 and the second variable resistance element 6 has an elongated shape,and the width-to-length aspect ratio of the element is 1 toapproximately 50 to 120. Further, the planar pattern of each of thefirst variable resistance element 5 and the second variable resistanceelement 6 is in a meandering or serpentine shape, and the most part ofthe planar pattern extends in the directions of Y1 and Y2, i.e., thedirections perpendicular to the fixing direction of the magnetization ofthe fixed magnetic layer 22. Since each of the first variable resistanceelement 5 and the second variable resistance element 6 has the elongatedshape extending mainly in the directions of Y1 and Y2, the baseresistance value of the element is set to be high.

In each of the first variable resistance element 5 and the secondvariable resistance element 6, when there is no action by the externalmagnetic field, the fixing direction of the magnetization of the fixedmagnetic layer 22 and the magnetization direction of the free magneticlayer 24 both correspond to the direction of X2. Therefore, theelectrical resistance value of the element is minimized. If a magnet orthe like approaches in the direction of X1 to provide the magneticdetection device 1 with a magnetic field directed in the direction ofX1, and if the strength of the magnetic field is increased to apredetermined amount, the magnetization direction of the free magneticlayer 24 is directed to the direction of X1. In this case, the fixingdirection of the magnetization of the fixed magnetic layer 22corresponds to the direction of X2, and thus the electrical resistancevalue of each of the first variable resistance element 5 and the secondvariable resistance element 6 is maximized.

FIG. 2B is the cross-sectional view illustrating the first referenceresistance element 4 and the second reference resistance element 7 cutalong a plane extending in the directions of X1 and X2. The firstreference resistance element 4 and the second reference resistanceelement 7 are the same in lamination structure. Similar to the firstvariable resistance element 5 and the second variable resistance element6, the first reference resistance element 4 and the second referenceresistance element 7 have a multilayer structure. The first referenceresistance element 4 and the second reference resistance element 7 arethe same as the first variable resistance element 5 and the secondvariable resistance element 6 in terms of materials and thicknesses ofthe respective layers forming the elements. However, the laminationorder of the nonmagnetic conductive layer 23 and the free magnetic layer24 is opposite between the first and second reference resistanceelements 4 and 7 and the first and second variable resistance elements 5and 6. In the layer structure of each of the reference resistanceelements 4 and 7, the antiferromagnetic layer 21, the fixed magneticlayer 22, the free magnetic layer 24, the nonmagnetic conductive layer23, and the protective layer 25 are laminated in this order from theside of the substrate 2.

The films of the reference resistance elements 4 and 7 and the variableresistance elements 5 and 6 are formed on the same substrate 2. Thus,the magnetization direction of the fixed magnetic layer 22 included ineach of the reference resistance elements 4 and 7 illustrated in FIG. 2Bis fixed in the direction of X2, in a similar manner as in the variableresistance elements 5 and 6 illustrated in FIG. 2A. In each of thereference resistance elements 4 and 7, however, the free magnetic layer24 is directly superimposed on the fixed magnetic layer 22. Thus, evenif the element is acted upon by the external magnetic field, the overallresistance value of the element does not change.

Further, the reference resistance elements 4 and 7 are the same as thevariable resistance elements 5 and 6 in layer structure and filmthickness. Therefore, a characteristic change caused by an ambienttemperature change or the like can be made equal between the referenceresistance elements 4 and 7 and the variable resistance elements 5 and6.

The first resistance adjusting unit 3 and the second resistanceadjusting unit 8 are the same in structure and planer pattern shape. Thefirst resistance adjusting unit 3 is provided between a leading end 4 aof the first reference resistance element 4 and a basal end 12 a 1 ofthe lead layer 12 a, while the second resistance adjusting unit 8 isprovided between a leading end 7 a of the second reference resistanceelement 7 and a basal end 13 a of the earth terminal 13.

The first resistance adjusting unit 3 and the second resistanceadjusting unit 8 are the same in structure. Thus, only of the firstresistance adjusting unit 3 is described below, and description of thesecond resistance adjusting unit 8 will be omitted. The components ofthe second resistance adjusting unit 8 will be denoted with the samereference numerals as the reference numerals used to denote thecomponents of the first resistance adjusting unit 3.

The first resistance adjusting unit 3 includes a first resistive layer31 and a second resistive layer 32, which extend parallel to each other.The first resistive layer 31 and the second resistive layer 32 are thesame in width, thickness, and overall length. The first resistanceadjusting unit 3 is the same in lamination structure as the firstreference resistance element 4 and the second reference resistanceelement 7 illustrated in FIG. 2B. Further, the respective layers formingthe first resistance adjusting unit 3 are the same in thickness as therespective layers forming each of the first reference resistance element4 and the second reference resistance element 7.

As illustrated in FIG. 1, the first resistance adjusting unit 3 includesconductive layers 33 a, 33 b, 33 c, 33 d, 33 e, 33 f, and 33 g toestablish conduction between the first resistive layer 31 and the secondresistive layer 32. The conductive layers 33 a, 33 b, 33 c, 33 d, 33 e,33 f, and 33 g are formed of conductive ink or the like containingcopper, silver, gold, or conductive filler including silver or gold. Thespecific resistance of the conductive layers 33 a, 33 b, 33 c, 33 d, 33e, 33 f, and 33 g is substantially lower than the average specificresistance of the first resistive layer 31 and the second resistivelayer 32. Further, the power supply terminal 11, the lead layers 12 aand 12 b, the earth terminal 13, the first output terminal 14, and thesecond output terminal 15 are also formed of a conductive materialhaving a substantially low specific resistance. The conductive layers 33a, 33 b, 33 c, 33 d, 33 e, 33 f, and 33 g may be formed of the sameconductive material as the conductive material forming the respectiveterminals 11, 13, 14, and 15 and the lead layers 12 a and 12 b.

As illustrated in FIG. 3, between the conductive layers 33 a and 33 b, aresistance element R1 is formed by a part of the first resistive layer31, and another resistance element R1 is formed by a part of the secondresistive layer 32. That is, a parallel portion including the parallelconnected resistance elements R1 and R1 is formed between the conductivelayers 33 a and 33 b. Further, between the conductive layers 33 b and 33c, resistance elements R2 and R2 are formed by the first resistive layer31 and the second resistive layer 32, respectively, and the mutuallyparallel resistance elements R2 and R2 form another parallel portion.

In a similar manner, a parallel portion including parallel connectedresistance elements R3 and R3 is formed between the conductive layers 33c and 33 d, and a parallel portion including parallel connectedresistance elements R4 and R4 is formed between the conductive layers 33d and 33 e. Further, a parallel portion including parallel connectedresistance elements R5 and R5 is formed between the conductive layers 33e and 33 f, and a parallel portion including parallel connectedresistance elements R6 and R6 is formed between the conductive layers 33f and 33 g. In the first resistance adjusting unit 3, the respectiveparallel portions from the parallel portion including the resistanceelements R1 and R1 to the parallel portion including the resistanceelements R6 and R6 are connected in series.

Each pair of the resistance elements R1 and R1 to R6 and R6 is formed bya part of the first resistive layer 31 and a part of the secondresistive layer 32, which have the same width and film thickness. Thus,the resistance elements R1 and R1 forming the same parallel portion havethe same resistance value. Similarly, the resistance value is the samebetween the two resistance elements forming each of the parallelportions, i.e., between the resistance elements R2 and R2, between theresistance elements R3 and R3, between the resistance elements R4 andR4, between the resistance elements R5 and R5, and between theresistance elements R6 and R6.

Further, the above-described conductive layers for establishingconduction between the first resistive layer 31 and the second resistivelayer 32 are disposed at different intervals. The interval between theconductive layers 33 b and 33 c is twice as long as the interval betweenthe conductive layers 33 a and 33 b. Further, the interval between theconductive layers 33 c and 33 d is twice as long as the interval betweenthe conductive layers 33 b and 33 c. Similarly, the interval between theconductive layers 33 e and 33 f is twice as long as the interval betweenthe conductive layers 33 d and 33 e.

As a result, the resistance value of the resistance element R2 is twiceas great as the resistance value of the resistance element R1. Further,the resistance value of the resistance element R3 is twice as great asthe resistance value of the resistance element R2, and the resistancevalue of the resistance element R4 is twice as great as the resistancevalue of the resistance element R3. Furthermore, the resistance value ofthe resistance element R5 is twice as great as the resistance value ofthe resistance element R4, and the resistance value of the resistanceelement R6 is twice as great as the resistance value of the resistanceelement R5.

FIG. 4 illustrates a circuit configuration of the first resistanceadjusting unit 3. In the present embodiment, the resistance values ofthe resistance elements R1, R2, R3, R4, R5, and R6 are 10Ω, 20Ω, 40Ω,80Ω, 160Ω, and 320Ω, respectively. Therefore, the combined resistance ofthe parallel portion including the resistance elements R1 and R1 is 5Ω,and the combined resistance of the parallel portion including theresistance elements R2 and R1 is 10Ω. Further, the combined resistanceof the parallel portion including the resistance elements R3 and R3 is20Ω, and the combined resistance of the parallel portion including theresistance elements R4 and R4 is 40Ω. Furthermore, the combinedresistance of the parallel portion including the resistance elements R5and R5 is 80Ω, and the combined resistance of the parallel portionincluding the resistance elements R6 and R6 is 160Ω. That is, thecombined resistance is sequentially doubled from one to the next of theparallel portions in the serial direction.

As illustrated in FIG. 3, the second resistance adjusting unit 8 is thesame as the first resistance adjusting unit 3 in the configuration ofthe resistance elements R1 to R6.

In the present magnetic detection device 1, a positive potential issupplied from a power supply to the power supply terminal 11, and theearth terminal 13 is grounded. When the magnetic detection device 1 isnot approached by a magnetic field, the resistance value of the firstvariable resistance element 5 and the resistance value of the secondvariable resistance element 6 are both at the lowest value. In thiscase, a midpoint potential obtained from the output terminal 14 isminimized, while a midpoint potential obtained from the output terminal15 is maximized.

If the magnetic detection device 1 is approached by a magnet, and thusif the magnetic field directed in the direction of X1 is increased, thedirection of the magnetic field of the free magnetic layer 24 includedin each of the first variable resistance element 5 and the secondvariable resistance element 6 is directed in the direction of X1. Thus,the resistance value of the first variable resistance element 5 and theresistance value of the second variable resistance element 6 aremaximized. As a result, the midpoint potential of the output terminal 14and the midpoint potential of the output terminal 15 are both maximized.If the difference between the potential of the output terminal 15 andthe potential of the output terminal 14 is taken by using a differentialamplifier, for example, a detection output of a wide variation range canbe obtained. When the output from the differential amplifier exceeds apredetermined threshold value, the approach of the magnet can bedetected.

To keep the change of the potential output from the output terminal 14and the change of the potential output from the output terminal 15within a predetermined standard range in consideration of therelationship of the changes with the threshold value, it is necessary toappropriately adjust the balance between the resistance value of thefirst variable resistance element 5 and the resistance value of thefixed resistor connected in series to the first variable resistanceelement 5. When there is no action by the external magnetic field, forexample, if the potential of each of the output terminals 14 and 15 isset to be one half a power supply voltage, the output from thedifferential amplifier can be made zero when there is no action by theexternal magnetic field.

In the present magnetic detection device 1, the potential output fromthe output terminal 14 can be adjusted by adjusting the resistance valueof the first resistance adjusting unit 3. Further, the potential outputfrom the output terminal 15 can be adjusted by adjusting the resistancevalue of the second resistance adjusting unit 8.

The resistance value of each of the first variable resistance element 5and the second variable resistance element 6 is approximately 1 kΩ to 3kΩ when no magnetic field is provided. The variation of the resistancevalue is approximately ±10%. In the present embodiment, the design valueof the resistance value of each of the first variable resistance element5 and the second variable resistance element 6 is 2 kΩ when no magneticfield is provided, and the variation of the resistance value isapproximately ±200Ω. Further, the resistance value of each of the firstreference resistance element 4 and the second reference resistanceelement 7 is set to be approximately 1.5 kΩ.

In the state as illustrated in FIG. 1 in which the films of the firstresistance adjusting unit 3 and the second resistance adjusting unit 8are not trimmed, the sum of the combined resistance values of each ofthe resistance adjusting units is 315Ω. Further, the maximum adjustmentrange of each of the first resistance adjusting unit 3 and the secondresistance adjusting unit 8 is 315Ω. Therefore, the design value of thecombined resistance value of the first reference resistance element 4and the first resistance adjusting unit 3 is 1815 to 2130Ω. Similarly,the design value of the combined resistance value of the secondreference resistance element 7 and the second resistance adjusting unit8 is 1815 to 2130Ω. In addition, each of the first resistance adjustingunit 3 and the second resistance adjusting unit 8 can change theresistance value thereof by the unit of 5Ω.

In this manner, it is possible to obtain a wide adjustment range of theresistance values in each of the first reference resistance element 4and the second reference resistance element 7. Further, when there is noaction by the magnetic filed, the voltage output from each of the outputterminals 14 and 15 can be easily adjusted to one half the power supplyvoltage, for example, by adjusting the resistance value by the unit of5Ω.

FIG. 5 shows, in a table, adjustment amounts of the resistance value ineach of the first resistance adjusting unit 3 and the second resistanceadjusting unit 8.

The leftmost column of FIG. 5 indicates the adjustment amounts of theresistance value in each of the first resistance adjusting unit 3 andthe second resistance adjusting unit 8. For example, the adjustmentamount is 5Ω in the uppermost row of the table. This means that theresistance value is increased by 5Ω. Meanwhile, the adjustment amount is315Ω in the lowermost row of the table. This means that the resistancevalue is increased by 315Ω. Further, the mark “◯” appearing in the tableindicates that a resistance element forming a parallel portion isbrought into the non-conduction state. That is, the uppermost row of thetable indicates that only one of the resistance elements R1 and R1forming a parallel portion is brought into the non-conduction state.Meanwhile, the lowermost row of the table indicates that one of theresistance elements R1 and R1, one of the resistance elements R2 and R2,one of the resistance elements R3 and R3, one of the resistance elementsR4 and R4, one of the resistance elements R5 and R5, and one of theresistance elements R6 and R6, which form the respective parallelportions, are brought in the non-conduction state.

As illustrated in FIG. 5, if only one of the resistance elements R1 andR1 forming a parallel portion is brought into the non-conduction state,for example, the resistance value of the first resistance adjusting unit3 or the second resistance adjusting unit 8 can be increased by 5Ω.Further, if one of the resistance elements R1 and R1, one of theresistance elements R2 and R2, and one of the resistance elements R3 andR3 are respectively brought into the non-conduction state, theresistance value can be increased by 35Ω. Furthermore, as in thelowermost row, if one of the resistance elements R1 and R1, one of theresistance elements R2 and R2, one of the resistance elements R3 and R3,one of the resistance elements R4 and R4, one of the resistance elementsR5 and R5, and one of the resistance elements R6 and R6 are brought inthe non-conduction state, the resistance value can be increased by 315Ω.

In this manner, the resistance value can be changed by the unit of 5Ω bybringing only one of the resistance elements included in each of theparallel portions into the non-conduction state and by combining theresistance elements to be brought into the non-conduction state.

One of the resistance elements R1 and R1 can be brought into thenon-conduction state by cutting off either one of the first resistivelayer 31 and the second resistive layer 32 between the conductive layers33 a and 33 b, for example. The same applies to the cases of the otherresistance elements R2 and R2 to R6 and R6.

The method of cutting off either one of the first resistive layer 31 andthe second resistive layer 32 includes cutoff using laser light, cutoffby milling, and cutoff by a photolithographic method, for example.Generally, the magnetic detection device 1 illustrated in FIG. 1 isobtained by forming a plurality of the magnetic detection devices 1 ofthin films on a common substrate and thereafter cutting the thus formeddevices into individual pieces. Thus, the magnetic detection devices 1formed in the same area on the same substrate have very similarcharacteristics. Therefore, after monitoring one of the magneticdetection devices 1 formed on the same substrate and then determiningwhich one of the resistance elements should be cut off, the adjustmentoperation of adjusting the resistance value can be performed in a singleprocess on the plurality of the magnetic detection devices 1 accordingto any one of the above-described methods.

Alternatively, as the method of bringing one of the resistance elementsR1 and R1 into the non-conduction state, the conductive layers 33 a and33 b may be formed to be connected to each other on a surface of eitherone of the first resistive layer 31 and the second resistive layer 32,for example.

Further, the first resistance adjusting unit 3 may be disposed betweenthe earth terminal 13 and the output terminal 14, instead of beingdisposed at the position shown in FIG. 3. Alternatively, the firstresistance adjusting unit 3 may be provided both at the position shownin FIG. 3 and between the earth terminal 13 and the output terminal 14.Similarly, the second resistance adjusting unit 8 may be disposedbetween the power supply terminal 11 and the output terminal 15, insteadof being disposed at the position shown in FIG. 3. Alternatively, thesecond resistance adjusting unit 8 may be provided both at the positionshown in FIG. 3 and between the power supply terminal 11 and the outputterminal 15.

1. A magnetic detection device comprising: a variable resistance element having an electrical resistance changed by an external magnetic field, and a reference resistance element having an electrical resistance unchanged by the external magnetic field, and serially connected to the variable resistance element, and applied with a direct current voltage to detect a midpoint potential between the variable resistance element and the reference resistance element, wherein at least one of the variable resistance element and the reference resistance element is serially connected to a resistance adjusting unit, including a plurality of serially connected parallel portions having a plurality of parallel connected resistance elements that are different from each other in combined resistance value, and wherein the sum of the combined resistance values of the resistance adjusting unit is adjusted by bringing any one of the resistance elements into a non-conduction state.
 2. The magnetic detection device according to claim 1, wherein the resistance adjusting unit includes a plurality of resistive layers extending parallel to each other and connected to each other by conductive layers at a plurality of positions, and portions of the resistive layers sandwiched between an adjacent pair of the conductive layers form the resistance elements forming one of the parallel portions, wherein the parallel portions differ from each other in combined resistance value by differently setting intervals between the conductive layers, and wherein the sum of the combined resistance values of the resistance adjusting unit is adjusted by disconnecting the resistance element at a position between the adjacent pair of the conductive layers.
 3. The magnetic detection device according to claim 2, wherein the variable resistance element is a magnetoresistance effect element, and each of the resistive layers forming the resistance adjusting unit is formed of the same film materials as film materials forming the magnetoresistance effect element, and a lamination order of the film materials is configured to prevent the resistance value thereof from being changed by the external magnetic field.
 4. The magnetic detection device according to claim 1, wherein each of the parallel portions is configured such that the plurality of the resistance elements are the same in resistance value, and the combined resistance value thereof is increased in a phased manner in the serial direction of the resistance adjusting unit.
 5. The magnetic detection device according to claim 4, wherein the combined resistance value of one of a pair of the parallel portions adjacent to each other in the serial direction is twice as great as the combined resistance value of the other one of the pair. 